1. Field of the Invention
The present invention relates to methods for disinfecting dental impressions. More particularly, it concerns the use of a pH-adjusted hypochlorite solution for killing microorganisms on dental impressions.
2. Description of the Related Art
It has been estimated that over 1,000,000 dental impressions are made each week in the U.S. Impressions are made of the teeth and soft tissues routinely by dentists for the fabrication of crowns, bridges, dentures, orthodontic appliances and many other dental appliances. Gypsum (plaster-like) materials are mixed and poured into the impression and allowed to harden. Once separated from the impression, the gypsum model is an exact duplicate of the patient's teeth and soft tissues. Guidelines from the American Dental Association (ADA), the Centers for Disease Control and Prevention (CDC) and the Occupational Safety and Health Administration (OSHA) require that every impression be disinfected after removal from a patient's mouth and before entering the dental laboratory in order to prevent contamination.
Disinfection of dental impressions is, however, a difficult task. In order to be considered useful, a disinfectant must effectively, and preferably inexpensively, kill the oral microorganisms that are carried on the impression without damaging the impression or reducing its accuracy. Existing disinfectants do not meet these criteria. Glutaraldehydes are often recommended for disinfection of impressions, however they vary greatly in effectiveness and are very expensive. In addition, glutaraldehydes are harmful to living tissue and may induce hypersensitivity, so gloves and other protective gear must be worn by personnel handling them (Naylor, 1992). Iodophores and phenolics are ADA approved for the disinfection of impressions, but are generally ineffective in this application (Westerholm et al., 1992; Schwartz et al., 1994). They have also been found to degrade the surface of some types of impression materials, producing poor quality gypsum models (Hilton et al. 1994). Phenolics are expensive, have a strong odor (requiring a well ventilated work area), and require protective gear (Naylor 1992). All of these disinfectants are less effective than the instant invention, are generally more expensive to manufacture, require longer immersion times, and ultimately produce gypsum models of lesser quality.
One of the least expensive but most effective disinfectants is aqueous sodium hypochlorite, commonly known as bleach. "Hypochlorites" are listed among the ADA's acceptable disinfectants. While sodium hypochlorite is quite effective in its commercially available form, a 5.25% solution in water (Beyerle et al., 1994; Westerholm et al., 1992), such a solution unfortunately etches some impression materials, resulting in a loss of surface detail (Vandewalle, 1994). If the solution is diluted, however, the damage to the impression is eliminated (Vandewalle, 1994), but the result is a concurrent loss of antimicrobial activity (Beyerle et al., 1994). These studies tested standard solutions of sodium hypochlorite, which has an inherent pH of about 12.
None of the products that are currently available for the disinfection of dental impressions are satisfactory. Most ADA approved disinfectants tend to be ineffective (Westerholm 1992; Schwartz et al., 1994) and expensive, cause degradation of some impression materials (Hilton et al., 1994), and have associated safety concerns (Naylor et al., 1992). An impression disinfectant that overcomes these problems would be a major advance in the art.